1. Field of the Invention
This invention relates to a system for identification, tracking and monitoring of the progress of process carriers containing batches of semiconductor wafers or memory disks through a variety of different processing operations at various locations within a plant facility and between different plant facilities using a bar code remote recognition system.
2. Description of the Prior Art
The semiconductor manufacturing industry requires that process carriers containing semiconductor wafers be moved through a manufacturing plant to a number of different locations where the semiconductor wafers are subjected to a variety of processing operations. Such operations include etching, cleaning, processing using photolithography operations, and subjecting to various other manufacturing, testing and processing operations. The manufacturing of memory disks similarly involves processing through a sequence of manufacturing operations within a manufacturing facility and between different facilities. In this industry, the wafers or memory disks are commonly handled in batches contained within carriers which are specifically designed to support the wafers or memory disks in the proper position for the manufacturing and processing machinery to either handle the disks or wafers while they remain in the carriers or alternatively remove them for a processing operation and then return them to the carrier. A batch, as defined and used hereinafter, means one or more (up to the capacity of the carrier) of the semiconductor wafers or memory disks.
As a process carrier containing a batch of wafers or memory disks moves throughout the manufacturing plant, it is desirable to track its progress through the manufacturing and processing operations. This has conventionally been done on a manual basis, either by generating paper records to track the progress of process carriers containing particular batches through these various operations or by some semi-automated system such as manual keyboard entry. A method and apparatus for monitoring the location of process carriers containing wafer disks has been disclosed in commonly assigned co-pending U.S. patent application Ser. No. 07/061,935, filed June 11, 1987, which involves the use of RF interrogation of coded surface acoustic wave transponder structures associated with the carriers for wafers or memory disks. However, it is desirable to provide a method for monitoring the location of disks and the carriers containing them which is reliable, involves low capitol investment, functions cooperatively with monitoring and tracking systems utilized in other fabrication areas within the industry, allows for rapid, reliable, non-contact monitoring and is impervious to attack by the various chemicals used in the processing of wafer disks. The present invention thus provides a location monitoring system which meets these requirements.
Methods of identifying, tracking and inventorying using coded bar code indicia have been in existence for about the past 15 years. Bar code indicia conventionally consist of a number of spaced apart parallel lines of varying widths. Data is coded in the width and spacing of the lines, so that when an optical probe is scanned across the code in a direction normal to the lines, a light beam in the probe is modulated in a manner which is unique to the particular code. The modulated light beam is directed and detected by an electro-optical detector and thereafter the resulting signal is processed and stored in an electronic computer.
Despite the length of time that bar code identification has been available, the application of bar code identifying, tracking and inventorying techniques to monitoring the location and progress of process carriers containing semiconductor wafers or memory disks through processing and manufacturing operations has not heretofore occurred. The application of bar coded systems to wafer or disk process carriers has not been implemented because of the harsh chemical and temperature processing environments to which these carriers are subjected under normal use conditions, which conditions would be destructive to most currently available bar code tags. Most currently available bar code tags are adhered to the substrate surface by adhesives. These tags and/or their adhesives would be readily deteriorated by the action of harsh chemicals. Also, although newer adhesives have reasonably good adherence to the surface of the process carriers, typically formed of TEFLON, even these newer adhesives are soon deteriorated by the chemicals used in processing. An acceptable bar code tag for process carriers must not be affected by chemical attack during the useful life of the carrier and must not contaminate or contribute to contamination of the chemical process baths.
This invention presents an encapsulation system for attaching a bar code tag to a process carrier, so that the tag is protected from the harsh chemical environment to which the carrier is to be subjected, while at the same time allowing the bar code indicia to be readily and accurately readable by conventionally available bar code scanners, preferably laser scanners.